Prior to colonoscopy, including virtual colonoscopy procedures, the colon must be cleansed so the surgeon may see any polyps and other lesions that are located on the interior surface of the colon. Additional cleansing procedures of the colon are carried out prior to radiological tests or surgical interventions. This cleansing generally entails the drinking of one or more cathartic solutions. Aqueous solutions of sodium phosphate salts (monobasic and dibasic sodium phosphate), such as FLEET® PHOSPHO-SODA®, are very effective oral cathartics and are extensively used prior to the above mentioned procedures. For pre-colonoscopy use, a split regimen is often preferred that includes one 45 mL dose given the evening before colonoscopy and a second 30 mL dose given at least three hours prior to the procedure on the following morning.
Ingestion of phosphate-rich medicaments, for example oral sodium phosphates solutions for bowel cleansing prior to a colonoscopy, has been found to induce significant increases in serum phosphorous concentration (18, 19). While normal ranges of serum phosphorous concentration fall between 2.5 and 4.1 mg/dl, patients given oral sodium phosphates solutions exhibit increases in serum phosphorous to an average of 7.2±0.6 mg/dl (18). These increases in serum phosphorous concentration were not affected by the administration of oral rehydration solution (ORS) (19).
Calcium phosphate crystal formation and concomitant decline in kidney function has been shown to be augmented in patients suffering from diseases which affect renal blood flow and glomerular filtration rate, such as ischemia-induced renal failure (5). Moreover, high phosphate diet has been shown to induce calcium phosphate crystal deposition in kidneys of normal rats, without impairment of renal function (6, 7). It was also shown that male Sprague-Dawley rats on high phosphate diet deposit calcium phosphate crystals in kidney tubules after being intermittently dehydrated. Furthermore, previous studies have suggested a predisposition of female rats to calcium phosphate crystal deposition following high phosphate diet.
Phosphate nephropathy consists of damage to kidneys caused by formation of calcium phosphate crystals or direct toxicity to cells within the renal tubules. The result is damage to the nephron, which can cause acute renal insufficiency or acute renal failure. A kidney biopsy in the setting of phosphate nephropathy typically shows the pathological findings of diffuse tubular injury with calcium phosphate crystal deposition.